|Swine Variant Cases Since 2011 - Credit CDC FluView Interactive|
Although we first learned of this case a week ago (see Indiana Reports H3N2v Infection In Fairgoer), the CDC posted their FluView summary of the case and a statement on their https://www.cdc.gov/flu/ website yesterday.
Cases (see map above) have been most common in the upper mid-west (Indiana & Ohio account for > 42% of all reported cases), but infection is likely under reported across the rest of the country.The incidence of swine variant flu infection is quite variable from year-to-year, with last year (see chart below) being the 2nd highest tally since surveillance began. It, however, pales in comparison to the 12 state outbreak of 2012 (see H3N2v Update: CDC Reports 52 New Cases, Limited H2H Transmission).
While most swine variant infections have been mild or moderate, a couple of deaths have been reported since 2012, along with a number of hospitalizations.
First the summary from yesterday's FluView report.
One human infection with a novel influenza A virus was reported by Indiana. This person was infected with an influenza A(H3N2) variant (A(H3N2)v) virus and reported indirect exposure to swine at an agricultural fair during the week preceding illness onset. The patient was a child < 18 years of age, was not hospitalized, and has fully recovered from their illness. No human-to-human transmission was identified. This is the first A(H3N2)v virus infection detected in the United States in 2018.
Early identification and investigation of human infections with novel influenza A viruses are critical so that the risk of infection can be more fully understood and appropriate public health measures can be taken. Additional information on influenza in swine, variant influenza infection in humans, and strategies to interact safely with swine can be found at http://www.cdc.gov/flu/swineflu/index.htm.
Additional information regarding human infections with novel influenza A viruses can be found at http://gis.cdc.gov/grasp/fluview/Novel_Influenza.html.
Although swine variant infection may seem fairly innocuous, these spillovers into the human population carry with them some risk, as these viruses (H1N1v, H1N2v, or H3N2v) have the potential to become more easily transmitted among humans.
While not expected to be as severe as some of the other novel viruses we are watching, immunity to these swine variant viruses is likely very low, and so the CDC's IRAT Influenza Risk Assessment Tool lists H3N2v as having moderate pandemic potential.Agricultural exhibits are very popular in both state and county fairs, but they do provide an opportunity for swine viruses to jump to humans (see EID Journal: Transmission Of Swine H3N2 To Humans At Agricultural Exhibits - Michigan & Ohio 2016).
While illness in pigs is only rarely reported, surveillance revealed an average prevalence of influenza A in fair pigs of 77.5%. The authors cautioned that this suggests `that subclinical influenza A infections in pigs remain a threat to public health (3).'The CDC is cautioning those at high risk of flu complications (children < 5 years, people > 65 years, pregnant women, and people with certain long-term health conditions) avoid pig and swine barns at fairs, while everyone else take commonsense precautions (no eating or drinking in pig barn, wash hands often, avoid sick pigs, etc.).
This from yesterday's Flu News & Spotlight. I'll return with a brief postscript.
July 6, 2018 – The first human infection with an influenza A(H3N2) variant (A(H3N2)v) virus was reported by CDC today. When influenza viruses that normally spread in swine are detected in people, they are called “variant” viruses and are designated with a letter v at the end of the virus subtype. The patient was a child < 18 years of age, was not hospitalized, and has fully recovered from their illness. Indirect contact with swine at an agricultural fair was reported in the week preceding illness onset. This infection is a reminder about important precautions that people should take at agricultural fairs to avoid the spread of influenza viruses between people and pigs.
This report brings the total number of reported A(H3N2)v infections in the U.S. since 2005 to 435. Swine flu viruses do not normally infect people; however, sporadic human infections with these viruses have occurred. Illness associated with variant virus infection includes symptoms similar to those of seasonal flu. Most illness has been mild, but as with seasonal flu, hospitalization and death can occur. There have been documented cases of multiple people becoming sick after exposure to one or more infected pigs and also cases of limited spread of variant influenza viruses from person to person.
In the United States, human infections with influenza A(H1N1) variant (A(H1N1)v), influenza A(H1N2) variant (A(H1N2)v), and A(H3N2)v have been detected. Most commonly, human infections with variant viruses occur in people with direct exposure to infected pigs (e.g., at a fair or at work), but transmission is possible without direct swine contact. Spread between pigs and people is thought to happen mainly when an infected pig (or human) coughs or sneezes and droplets with influenza virus in them spread through the air. If these droplets land in the nose or mouth, or are inhaled, that person (or pig) could be infected. There also is some evidence that the virus might spread by touching something that has virus on it and then touching the mouth or nose. A third way to possibly get infected is to inhale particles containing influenza virus. Influenza has not been shown to be transmissible to people through eating properly handled and prepared pork (pig meat) or other products derived from pigs.
Human infections with novel influenza viruses (i.e., those that do not normally circulate in humans) should be fully investigated to be sure that such viruses are not spreading in humans in an efficient and ongoing way, and to limit further exposure of humans to infected animals if infected animals are identified. CDC has been in communication with Indiana public health officials; the epidemiology of the variant virus infection reported recently is consistent with past reports.
Agricultural fairs take place across the United States every year, primarily during the summer months and into early fall. Many fairs have swine exhibitions, where pigs from different places come in close contact with each other and with people. These venues may magnify the risk of spread of influenza viruses between pigs and people.
Some people are at high risk of developing serious illness from variant virus infections, just as they are from seasonal influenza. This includes young children, people with underlying health conditions like asthma, diabetes or heart disease, pregnant women and people who are 65 and older.
In order to reduce the possible risk of serious illness to people posed by interactions between people and pigs at fairs, CDC recommends that people at high risk for serious flu complications avoid pigs and swine barns at fairs.
Precautionary measures for people who are not in a high risk group[1.3 MB, 2 pages] include not taking food or drink into swine barns, avoiding swine that look or act sick, and handwashing after swine exposure.
Seasonal flu vaccines are not formulated to protect against variant viruses, but the same influenza antiviral drugs used to treat seasonal flu can be used to treat variant virus infection in children and adults. The currently recommended drugs – oseltamivir, peramivir, and zanamivir – are available by prescription only. Early treatment works better and is especially important for people who are very ill or who are at high risk of serious flu complications.
CDC has information and guidance for local and state public health officials regarding the surveillance and investigation of human infections with A(H3N2)v virus, and will share updated information if the situation changes.
Swine flu viruses circulate all over the world, although surveillance in most places is minimal at best. How many human infections, and how many different variants there are in circulation, is unknown.
Some of these viruses, such as the EAH1N1 virus in China, are viewed as having significant pandemic potential. A few of my recent blogs on swine variant influenza outside the United States include:
Trans. & Emerg. Dis.: Appearance Of Reassortant European Avian‐origin H1 influenza A viruses in Swine - Vietnam
I&ORV: Triple-Reassortant Novel H3 Virus of Human/Swine PNAS: The Pandemic Potential Of Eurasian Avian-like H1N1 (EAH1N1) Swine Influenza